Originally Posted by CliftonGK1
The fun way to do it would be with EL wire. If you're handy with a wirestripper and soldering gun, you could outline a whole helmet with EL wire or EL tape. It would be lightweight, takes little juice to power it, and would be very bright.
Another option is flat-mount LEDs. Again, handy with a soldering iron is a big requirement.
What started out as a half-joke might actually work. Here's a link to some EL wire. The outdoor stuff is $1.30 per foot. A small light waterproof battery box at the back of the head could work.
http://www.coolight.com/category-s/54.htm